JP2002069226A - Process for producing urethane foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a urethane foam having proper vibration transmitting characteristics with almost no change in the composition thereof. SOLUTION: In making a seat for vehicles, a urethane foam material is foam-molded, and the urethane foam after demolding is subjected to such a foam breaking processing for controlling the residual cell membrane as to pass it through gaps between crush rollers in two or more steps different in interspace, thus controlling the vibration transmitting characteristics of the urethane foam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving the vibration transmission characteristics of urethane foam used, for example, as a cushion material for a vehicle seat or the like.

[0002]

2. Description of the Related Art Conventionally, foamed products as a synthetic resin molded product obtained by pouring a flexible polyurethane foam foam molding material into a molding die and foaming and molding the same are used as cushioning materials for vehicle seats and interior parts for automobiles. Many are used. Above all, since the vibration transmission characteristics of the vehicle seat have a great influence on the ride comfort of an automobile, it is necessary to design a material having appropriate vibration transmission characteristics. FIG.
Is a diagram showing the resonance characteristics of urethane foam having closed cells called HR having a standard blending composition, which is generally used for a vehicle seat. In a vehicle seat, generally,
It is said that the higher the vibration absorption around 6 Hz (4-8 Hz), which is called the resonance point of the internal organs, the better the riding comfort. Therefore, a method of increasing the rebound resilience of the urethane foam and lowering the resonance frequency to increase the vibration absorption around 6 Hz, which is a frequency band sensitive to the human body, can be considered.

[0003]

However, simply increasing the rebound resilience and lowering the resonance frequency does not provide the same effect as in FIG.
As shown by the broken line, the vibration absorption around 6 Hz is higher than that of the standard compound, but on the contrary, the resonance magnification in the low frequency region increases. Therefore, there is a problem that the input vibration is amplified particularly in the frequency band of 1 to 3 Hz, and the riding comfort is rather deteriorated. Therefore,
It is conceivable to increase the damping characteristics by changing the composition of the urethane foam material and improve the vibration transmission characteristics.
The change of the composition not only involves enormous man-hours in actual production equipment, but also has the possibility that other resin properties such as elongation and durability may be significantly changed. In general, when a low resilience material is used as the urethane foam, the resonance frequency tends to increase, and as shown by the dashed line in FIG. 6, the vibration absorption characteristics in the frequency band of 1 to 3 Hz are improved. However, on the other hand, the vibration absorption around 6 Hz is deteriorated. In addition, low resilience foam materials generally have the problem of poor durability.

The present invention has been made in view of the conventional problems, and has as its object to provide a method for producing a urethane foam having appropriate vibration transmission characteristics without substantially changing the composition of the urethane foam. Aim.

[0005]

According to a first aspect of the present invention, there is provided a method for producing a urethane foam, comprising: controlling a vibration transmission characteristic of the urethane foam after foaming and molding a foamed urethane foam material; It is characterized by performing a foam breaking process to perform
Omitting the complicated work of changing the composition, lowering only the resonance magnification without substantially changing the resonance frequency,
It is possible to secure the vibration absorption around 6 Hz and to improve the vibration absorption in the low frequency band.

The urethane foam manufacturing method according to the second aspect is characterized in that the vibration transmission characteristics of the urethane foam are manipulated only by the foam breaking treatment without changing the composition of the urethane foam foam molding material. I do.

According to a third aspect of the present invention, in the method for producing a urethane foam, the demolded urethane foam is subjected to a foam breaking treatment for passing between crush rollers to control the residual ratio of the cell membrane of the urethane foam. It is characterized by.

In a fourth aspect of the present invention, the method for producing a urethane foam is characterized in that the foaming treatment is performed by passing between a plurality of crash rollers.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an outline of a method for manufacturing a vehicle seat according to the present embodiment.
A liquid polyurethane mainly composed of an isocyanate component and a polyol component is injected into a mold cavity, foamed and molded, and then demolded to obtain a soft urethane foam. Next, the demolded urethane foam is successively passed between the rollers 4 to 9 of the crush rollers 1, 2, and 3 having intervals of 50 mm, 40 mm, and 20 mm, respectively, to perform a bubble breaking treatment, and the residual ratio of the cell film is reduced. By controlling the air inflow / outflow resistance (air permeability) of the urethane foam by controlling, only the resonance magnification is reduced without substantially changing the resonance frequency. In addition, although the said foam breaking process is normally performed in order to prevent the shrinkage of the foam after demolding, in this embodiment, since the residual ratio of the cell film is controlled by changing the crash conditions, It is possible to obtain a urethane foam having a lower air permeability and a lower rebound resilience than the above standard blended product. Conversely, it is also possible to increase the air permeability and increase the rebound resilience.

Here, the vibration transmission characteristics of urethane foam will be described. FIG. 2 is a diagram showing a vibration model of urethane foam. The urethane foam is approximated by a mathematical model in which a mass m is connected in parallel to a spring (spring constant k) and a dashpot (damping coefficient c). Can be. In order to change the damping characteristic of the urethane foam, it is necessary to change the value of the dashpot damping coefficient c in the above model. However, in the conventional operation of changing the composition, it is difficult to change only the damping coefficient c, and the spring constant k also changes at the same time.
As a result, for example, when the resonance peak (resonance magnification) is lowered as in the case of using the above low resilience material, the resonance frequency is increased. For example, the resonance magnification and the resonance frequency are changed independently. Could not.

[0011] The inventors have proposed that the urethane foam after releasing the mold be separated by a roller spacing of 10, 20, 30, 40 mm, respectively.
It was found that by passing through a crush roller and performing bubble breaking processing with different degrees of compression, as shown in FIG. 3, only the resonance magnification could be changed with little change in the resonance frequency. This is because if the residual ratio of the cell membrane is controlled to change the inflow / outflow resistance (air permeability) of the urethane foam, the dashpot of the above mathematical model is hardly changed without changing the composition of the urethane foam. This indicates that only the attenuation factor c can be manipulated to reduce only the resonance magnification. In the present embodiment, by changing the crash condition, the air permeability after the crash process is reduced and the damping coefficient c is increased, so that, as in the case of using the low resilience material described above, It is possible to obtain a urethane foam having almost the same elongation, durability, and resonance frequency as those of the conventional standard compound, and having only a low resonance magnification, without changing the compounding that may adversely affect the physical properties of the molded product.

FIG. 4 shows the resonance characteristics of the urethane foam (product of the present invention) produced by the above method.
As shown in the figure, a 400 × 400 × 70 t rectangular sample 10 was mounted on a vibration table 11, and a 50 kg iron plate (pressing plate) 12 was placed thereon, and the amplitude ± 2.5 mm, A sine wave vibration having a frequency of 1 to 10 Hz was applied for 5 minutes, and the vibration transmission characteristics were measured using the displacement meters 13 and 14. As a comparative example, a standard compound (Comparative Example A;
The resonance characteristics of a thin solid line), a high resilience compound (Comparative Example B; dashed line), and a low resilience compound Comparative Example C; dashed line) are also shown. The anti-elasticity of the product of the present invention is 61%, the standard compound is 68%, the high resilience compound is 78%, and the low resilience compound is 58%.
%. As is clear from the figure, the product of the present invention has almost the same resonance frequency as the standard compound, but the resonance magnification is 2,2, which is about half or less of the standard compound, and is 1 to 3 Hz. It was confirmed that both the low frequency range and the vibration absorption characteristics near 6 Hz can be improved. Also,
Since the resonance frequency of urethane foam depends on its shape,
Although the actual vehicle seat resonance frequency and the sample frequency are slightly different, it is easy to apply the above results to an actual vehicle seat and reduce only the resonance magnification while keeping the resonance frequency unchanged. Yes, 6Hz
It is possible to manufacture a vehicle seat with good ride comfort, which has good vibration absorption in the vicinity and improved vibration absorption characteristics in a frequency band of 1 to 3 Hz. In the vehicle seat, the resonance magnification is desirably 3 or less in terms of riding comfort.

In the above-described embodiment, the crash processing by the three-stage roller is performed. However, the present invention is not limited to this. The urethane foam may be tied and passed between the rollers. The number of passes and the crash conditions such as spacers are appropriately determined by the shape and composition of the urethane foam. Further, even if the composition is the same, by changing the crash condition, the residual ratio of the cell film is controlled to change the air inflow / outflow resistance (air permeability) of the urethane foam, thereby controlling the damping coefficient c, and It is also possible to produce urethane foams having different transfer characteristics. The same effect can be obtained by performing a bubble breaking process by a vacuum crash instead of the roller crash. In this case, the residual ratio of the cell film is controlled by changing the degree of vacuum, the speed at which the pressure is returned to the normal pressure, the number of crashes, and the like.

[0014]

As described above, according to the present invention,
After foaming and molding the urethane foam foam molding material and demolding, the urethane foam is subjected to a foam breaking treatment for controlling the residual ratio of the cell film and controlling the vibration transmission characteristics. Without changing the vibration transmission characteristics of the urethane foam. In other words, even if the composition is the same, any vibration transmission characteristics can be manipulated by changing the bubble breaking treatment conditions in the subsequent process, which requires a great deal of man-hours and may adversely affect the physical properties of the molded product. It is possible to improve the vibration transmission characteristics of the urethane foam without making any compounding change.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a method for producing a urethane foam according to the present embodiment.

FIG. 2 is a mathematical model that approximates the vibration state of urethane foam.

FIG. 3 is a diagram showing a change in resonance magnification depending on a roller interval.

FIG. 4 is a diagram showing resonance characteristics of the urethane foam of the present invention.

FIG. 5 is a diagram showing a method for measuring the resonance characteristics of urethane foam.

FIG. 6 is a diagram showing resonance characteristics of a conventional urethane foam.

[Explanation of symbols]

1,2,3 Crash roller, 4 ~ 9 roller, 10
Urethane foam sample, 11 Shaking table, 12
Pressure plate, 13, 14 Displacement meter.

Claims (4)

[Claims] 1. A foamed urethane foam molding material.
A method for producing a urethane foam, characterized in that, after molding and demolding, the urethane foam is subjected to a foam breaking treatment for controlling vibration transmission characteristics. 2. The urethane foam production according to claim 1, wherein the vibration transmission characteristics of the urethane foam are manipulated only by foam breaking without changing the composition of the urethane foam foam molding material. Method. 3. The method for producing a urethane foam according to claim 1, wherein the demolded urethane foam is subjected to a foam breaking treatment for passing between crush rollers. 4. A bubble breaking process is performed by passing between a plurality of crash rollers.
3. The method for producing a urethane foam according to 1.).